The invention relates to a process for producing a plastic casing reinforced against tensile forces by, elements for resisting extension in the plastic casing. The process includes the elements being extruded in molten form at the same time as the plastic casing serving to receive these elements is extruded.
In many cases in which plastic is used as a casing or walling material, the strength value of most plastics does not satisfy the demands made on the casing. Therefore, it is known, for example for plastic insulations for electrical and/or optical cables or lines, to incorporate in the insulation or to bond in a suitable form with the insulation elements for resisting extension (German Patent 2,740,162, German Patent 2,818,297). In such cases, the elements for resisting extension have been placed on or under the insulation and, for example, are adhesively bonded with the insulation, jacket or casing. Processes are also known in which the elements for resisting extension have been fed to the insulation during extrusion.
JP-A-62,130,821 discloses a process in which a tubular body is extruded, reinforcing filaments which may consist, for example, of LCPs and are also embedded in the tube walling being extruded in coextrusion by means of tubular dies. These reinforcing filaments run in straight lines, which may be disadvantageous for some applications, for example in the case of strong bending stresses, in the case of stranding operations, etc.
Also to be cited in this connection as prior art are U.S. Pat. Nos. 4,553,815 and 4,767,183, in which although the use of LCPs reinforcing against tensile forces is already described in the case of optical cables, their simultaneous extrusion is not.